Focus magazine said an analysis by German security services showed Merkel’s calls were listened into by even more people than initially thought.

It said analysis by German security services showed the four countries, and not just the US, were eavesdropping.

The British Embassy in Berlin declined to comment on the allegations.

Relations between Germany and the US have turned chilly since it was alleged that its National Security Agency (NSA) has been tapping Merkel’s phone, possibly from a listening station on top of the US embassy which is just a few hundred metres away from the Chancellor’s office in the centre of Berlin.

Focus, meanwhile, also reported that as well as targeting Merkel’s phone, Russian spies were particularly active in Germany with 120 agents operating in the country.

US officials arrived in Berlin on Monday to meet the German foreign minister over the NSA spying scandal.

One of the officials said the United States was taking German outcry over revelations of American spying on Europeans seriously, ahead of his visit to soothe frazzled ties.

Congressman Gregory Meeks told Handelsblatt newspaper that US-German relations were “of enormous importance” and must be stronger and closer still.

“We want the Germans to know that we don’t take their anger lightly,” Meeks said in comments reported in German and made before his trip together with Senator Chris Murphy, who chairs the Foreign Relations Subcommittee on European Affairs.

They were scheduled to meet the German foreign and interior ministers on Monday before heading to Brussels on Tuesday.

Germans have reacted angrily to revelations that emails, phone calls, web searches and other data may have been hoovered up by US intelligence agents, as part of widespread espionage that has also strained Washington’s ties with other partners.

After meeting the US delegation Monday, Thomas Oppermann, the Social Democrats’ parliamentary group leader and chairman of the secret service oversight committee, said the US espionage affair was “not over”.

“We expect further light to be shed,” he said, adding there had been agreement between the parties “that the completely out-of-hand practice of bugging by the NSA must finally have limits”.

Merkel called in parliament last week for answers over “grave” US spying accusations which, she said, were testing transatlantic ties, including fledgling US-EU trade talks.

“We understand the German fears,” Meeks said, adding that US President Barack Obama was also “very concerned”.

“For this reason he’s having checked which secret service methods are reasonable and which are not,” he added.